10 20 40 60 cm

mittakaava < 10 cm

         
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Gösta Sundman: Suomen Kalat (Kansalliskirjasto, The National Library of Finland), Lauri Urho, Petri Savola (Uudenmaan ympäristökeskus)

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Three-spined stickleback

Gasterosteus aculeatus

  • Family: Sticklebacks and tubesnouts – Gasterosteidae
  • Similar species: brook stickleback, nine-spined stickleback
  • Size: 4-7 cm, max. 9 cm.
  • Appearance: Body tapers to a very narrow caudal peduncle leading to a fan-shaped caudal fin – features typical of the sticklebacks. The three-spined stickleback is larger and deeper-bodied than Finland’s other sticklebacks. Sides have tall, narrow bony plates varying greatly in number from 4-5 behind the operculum to more than 30 along the entire side. True to its name, there are three spines anterior to the dorsal fin. The first two spines are prominent, the third smaller. Spines show remnants of fin membrane posteriorly. The pelvic fins have virtually been replaced by spines, which can be erected and locked in position.
  • Colouring: Back greenish and sides silvery. At breeding time the male develops a bright red throat and belly, lower part of operculum may show dark patches.
  • Reproduction: Spawns in June. Some may over-winter at sea and ascend rivers to spawn. Males establish a territory, which they defend aggressively. The male builds a nest from pieces of plant material and entices females to lay by displaying his handsome red belly. After fertilising the eggs the male stands guard, occasionally fanning the eggs with well-oxygenated water until they hatch after about a week.
  • Food: Chironomid larvae and other small invertebrates.
  • Distribution and habitat: The three-spined stickleback can be found in both brackish water and freshwater. Common along all of Finland’s coasts. In inland waters, the species is found at least in lake Pyhäselkä and the river Pielisjoki, and even in the Utsjoki and Inari areas of northern Lapland. Outside the breeding season, three-spined stickleback move in shoals. Large shoals appear in late summer in outer parts of the archipelago off SW Finland. Winters are spent in deeper water.
Other species from the same family

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